The invention relates to backing up computer data on a host computer storage disk.
Computer data are often backed up, i.e., copied, to a storage medium other than the host computer's storage disk, to permit the recovery of the data as they existed at some point in time in the event of system failure or inadvertent loss of data. The data can be automatically backed up on a daily or other periodic basis and stored on tape or optical archive media.
With some desktop personal computers, backup is done manually on an erratic schedule, with the user of the desktop being responsible for keeping track of the backup media. There are backup applications that provide backup for data stored on a desktop computer by writing to diskettes or to an additional tape or disk drive associated with the computer. These applications can have a facility for automatic backup but rely on the user to put new media into a tape drive.
In general there are two ways to back up data: physical level backup and logical level backup. The term "physical level" refers to the data as stored at specific locations on some physical media such as a host computer disk. The term "logical level" refers to the data as seen by the user application programs in files or database tables. Typically the computer's operating system (e.g., UNIX or DOS) includes a file system that does mapping between the physical level and the logical level. Physical level backup involves making a raw copy from a computer disk to an archive medium without going through the file system or other physical to logical interpreter. Logical level backup involves using an interpreter (e.g., a file system) while doing backup to do physical to logical mapping.